There has long been a need for capacitors which can be manufactured in a simple and inexpensive manner, especially for incorporation into printed circuits. More recently, an increasing need has arisen in this regard, resulting from the use of capacitive input keyboards for data-processing systems. German Offenlegungsschrift No. 2,744,206 relates to a capacitive key, which is intended to be used for a key field of this type, but the capacitor, as such, is assembled in a conventional manner from mechanical parts must be made capable of being moved with respect to one another.
The manufacture of capacitors, involving the application, to a greater or lesser extent, of printed-circuit techniques is already known. A capacitive network is known from German Offenlegungsschrift No. 2,841,742, especially for use as a capacitor-cascade arrangement in voltage-multipliers, in which network metal layers which serve as capacitor foils and terminals are printed on a base plate, this plate forming the dielectric of the capacitor. By stacking dielectric plates of this type, one upon another, with printed-on metal layers and metallized layers for appropriately interconnecting the individual layers, a stacked arrangement is obtained, containing, for example, parallel-connected or series-connected capacitors. However, this design, which uses pre-existing dielectric plates as the dielectric of the capacitor, is not very suitable for incorporation into printed circuits, in which the overriding aim is to produce all parts having electrical functions by means of layers on a substrate plate, or on a carrier plate. Similar considerations apply in the case of known designs of capacitors in which thin metal plates are used as capacitor foils, a feature which likewise does not lend itself to integration into printed-circuit technology, which essentially employs only printing steps or etching steps.
A capacitor which can be manufactured by the screen printing process is already known from German Offenlegungsschrift No. 2,132,935. This capacitor is manufactured by printing a silver paste, as the base electrode of the capacitor, onto a carrier plate. The paste is baked-on, accompanied by evaporation of the carrier agent. Next a screen-printable dielectric paste is applied as a thick-film dielectric, this paste containing a glass or ceramic frit in an organic carrier agent, for example in a solution of ethyl cellulose in terpineol, which is then fired at temperatures between 800.degree. C. and 1,000.degree. C. A silver paste is then applied to the dielectric, as the counter-electrode of the capacitor. This paste is fired at a temperature below 780.degree. C.
This known design of a thick-film capacitor has the disadvantage that, on account of the high firing temperature, in the region of approximately 1,000.degree. C., it is restricted to refractory carrier materials, such as, for example, Al.sub.2 O.sub.3. Refractory carrier plates of this type, made, for example, of Al.sub.2 O.sub.3, cannot be kept perfectly flat when their superficial dimensions are sufficiently large to permit the manufacture of large-area input keyboards with a comparatively large number of capacitors and the terminal and connecting leads associated therewith. Moreover, plates of the required size are prohibitively expensive. Further, the use of capacitor-electrodes, produced by printing-on and baking-of silver pastes, entails the disadvantages that there is a risk of the silver migrating during the firing operations and/or during subsequent service. Finally, metallized layers of this type, derived from silver pastes, cannot be soldered without difficulty.